Fibromyalgia syndrome (FMS) is an insidious disease that results in disability for 70% of those who suffer from it and tremendous loss of work and productivity. It is estimated that 8-12 million adults in the U.S. are affected by FMS, making it the most common chronic widespread pain syndrome. The exact mechanisms leading to the development and maintenance of fibromyalgia are unknown. But, accumulating evidence suggests abnormal nociceptive processing in the central nervous system (CNS) that could result from aberrations in supraspinal modulation. Our laboratory has developed procedures to assess supraspinal modulation of physiological and subjective nociceptive reactions (nociceptive flexion reflex, skin conductance, heart rate, pain report). A standardized picture-viewing paradigm is used to experimentally manipulate emotional valence (unpleasant, neutral, pleasant), and physiological-emotional manipulation checks verify emotional reactions. During picture-viewing, noxious electric stimuli are delivered (balanced across picture valence) and nociceptive reactions are recorded and averaged by picture valence. In healthy controls, we have shown that nociceptive reactions are reliably modulated in parallel by picture valence. Unpleasant pictures facilitate nociceptive reactions and pleasant pictures inhibit nociceptive reactions (an effect that explains 47-52% of the combined variance in the reactions). Because the nociceptive flexion reflex (a spinal reflex) is modulated, this suggests descending modulatory circuits are involved. Therefore, these procedures provide a non-invasive way to study supraspinal modulation. The present study will use the picture-viewing paradigm to study supraspinal modulation in FMS patients, rheumatoid arthritis (RA) patients, and no-pain controls. RA patients provide important controls for chronic pain history and other comorbid variables (eg, psychological distress, health/physical functioning, maladaptive coping) that could influence the emotion-pain relationship. Also, emotional factors are important in RA and FMS pain, but it is unclear whether emotion plays an equally potent role in both conditions. Further, there is limited human evidence for dysfunctional supraspinal modulation in RA, although RA is also associated with hyperalgesia. The specific aims of this study are: (1) To examine supraspinal modulation of nociceptive reactions in FMS patients and (2) To assess for hyperalgesia in FMS and RA patients.